Lithium in the form of lithium carbonate is administered to manic-depressive patients. The therapeutic range of lithium ion in plasma is quite narrow, namely, 0.8 to 1.2 mM. It is important to monitor the lithium level in such patients because of the toxic side effects that appear when the lithium level in blood exceeds the recommended level.
Lithium is determined quantitatively using solution assays and ion-selective electrodes. Dyes, such as 14-Crown-4-ether derivatives are known for use in such assays. Japanese Kokai 62/72683 (1985) discloses a class of such dyes that act as colorometric reagents in extracting lithium and as useful as charge transport carriers for ion-selective electrodes. The problem is that the disclosed dyes cannot be adapted for use in dry analytical elements. It would be desirable to have dyes that could be used to make dry analytical elements for assaying lithium.